Measurement of the membrane flexibility in lamellar and ''sponge'' phases of the C(12)E(5)/hexanol/water system

The present work is primarily concerned with the measurement, by several different methods (using X-ray and static Light scattering experiments of dynamic light scattering experiments), of the elasticity of bilayers made up of n-dodecyl pentaethylene glycol monoether (C(12)E(5)) and hexanol molecules. The membrane bending elasticity modulus, kappa, has been measured for both the L(alpha) (lamellar) and the L(3) (''sponge'') phase of the C(12)E(5)/hexanol/water system. For the lamellar phase, kappa was measured using both the escess area and the dynamics of the fluctuations, while for the sponge phase kappa was measured using only the excess area. The values of kappa measured seem to be of the same order (approximately k(B)T) for both the lamellar phase and the sponge phase, although the molar ratio of hexanol to C(12)E(5) is 4 times bigger in the sponge phase. The effect of temperature on kappa was also studied: the slight increase in kappa found for this system with temperature seems to be related to a decreasing polar head area of the C(12)E(5) molecules. For the sponge phase, kappa cannot, be measured from the dynamics of the fluctuations; however, some results; can be extracted from the dynamic light scattering experiments. The most interesting one was that the collective diffusion coefficient D is proportional to the membrane volume fraction, phi(m), and is a function of the membrane elastic constants, kappa and kappa, as well as of the thermal energy k(B)T, leading to an estimate of kappa.